Selenium rectifier



Oct- 11, 1950 A. KLEINLE ETAL 2,956,218

SELENIUM RECTIEIEE Filed sept. 17, 1957 2,956,218 Patented oet. 11,1960

SELENIUM RECTIFIER Alois Kleinle, Numberg, and Rdolf Friedrich Weiss,

Roth, near Numberg, Germany, assignors to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 17, 1957, Ser. No. 684,487 Y Claims priority, application Germany Oct. 5, 1956 6 Claims. (Cl. 3177-4241) This invention relates to selenium rectifiers having substantially improved electrical properties, and to a method of producing such rectifiers.

Selenium rectifiers generally consist of a metallic base electrode, a selenium layer evaporated onto the base electrode, and a counter electrode deposited onto the selenium layer. In the selenium layer, which is adjacent the counter electrode, there is formed the so-called barrier layer, which substantially determines the electrical properties of the rectifier. It is known to apply intermediate layers of particular chemical compounds between the selenium and the base electrode, to reduce the transient or contact resistance therebetween. It is also known to treat the surface of the selenium with salts, solutions or liquids, prior to the deposition of the counter electrode, for improving the blocking or barrier properties.

It is further known to add to the selenium, halogen and halogen compounds, to increase the electrical conductivity of the Selenium. Additives such as thallium may be added to the counter electrode metal, to provide a barrier layer having improved blocking ability.A It is yalso known to provide a thin layer of one of the metals thallium, indium or gallium, between the selenium and counter electrode to increase the lblocking ability of the rectifier plate.

In the conventional types of selenium rectifiers, however, the resistance of the selenium layer is a relatively high one which is undesirable. Of course, by means of the aforementioned additions to the selenium it is possible to slightly diminish the resistance, but it has been impossible to make the forward resistance of the rectiiier plate smaller than about 2.5 to 3.5 ohms/cm?.

Accordingly, an object of the present invention is to reduce the forward resistance of the rectifier without deteriorating the other rectifier properties.

According to the invention this is accomplished by adding gallium to the selenium in addition to the conventional additions of halogen.

By means of these additions there is obtained surprisingly, a substantial reduction of the selenium resistance. Consequently, the quality of the rectifier plates is improved greatly, without a deterioration of the blocking properties. Deterioration is usually the result when adding conductivity-increasing additives. In accordance with the invention the forward resistance of the selenium can be reduced to almost l ohm/cm?. This is particularly important when it is considered that most often a plurality of rectifier plates are arranged in series.

In order to reduce the resistance of the selenium, gallium may be added in an amount up to 10 mg. percent, that is, l0 mg. of gallium to 100 g. of selenium. Of a particular advantage is the combination of chlorine and gallium in the selenium. The contents of chlorine in the combination should be appropriately chosen to amount to about mg. percent.

A further advantage is obtained when the gallium iS only added to one portion of the selenium layer. The

selenium layer is compiled of several layers and the addition of gallium is preferably added to the seleniumlayer next to the base electrode. Thus, lfor instance, the selenium layer may consist of two layers,`the layer next to the base electrode containing, gallium, and the layer lyingA next to the counter electrode being free of gallium. In

addition to the gallium, a halogen, preferably chlorine, has to exist inthe selenium for achieving the desired effect. The galliumless selenium layers only contain the halogen additives. Y

In one theoretical work on the resistances of selenium, selenium containing an'addition of gallium has been examined. lIn this study, however, it has been found that only the resistance of the pure selenium had Ibeen affected. The study concluded that indium has the `same effect. Selenium layers, however, with a simultaneous addition of gallium and halogen have not yet been examined, and the result obtained in accordance with the invention is completely surprising in light of the examinations which of three layers, wherein the middle one contains gallium has certain advantages. In this case the selenium layer I, adjacent the base plate is free of gallium and is dimensioned to4 be thinner than the selenium layer adjacent the counter electrode which is also free of gallium. Outstanding results are obtainable when a selenium layer with a l5-20p. thickness is applied to the base electrode, and when on this layer there is arranged a selenium layer containing gallium with a thickness of about 10;; and on which there is again deposited a gallium free selenium layer with a thickness of 30-40/t.

The described Sequences of layers of gallium-free and gallium-containing selenium may also be repeated several times.

Further, it is of advantage when the concentration of the gallium in the selenium layer decreases from the base electrode towards the counter electrode. This, by way of example, can be accomplished in that the concentration of the gallium decreases steadily, or in that the gallium concentration of the individual gallium-containing layers decreases towards the counter electrode. In either case, however, it is important that the selenium layer adjacent the counter electrode contains as little as possible of the gallium.

The introduction of the gallium into the selenium layer i is best provided by simultaneously evaporating gallium and selenium. These two substances should be evaporated in separate evaporators, in order to achieve the desired result. Metallic gallium or gallium compounds may be added to the selenium. For example, a halogen compound of the gallium, such as gallium chloride may be used. By selectively regulating the heating of the evaporator for the gallium it is possible to produce the desired `distribution of the gallium in the selenium layer.

The contact resistance between the selenium and the base electrode may be reduced still further by applying the known intermediate layers between the base 'electrode and the selenium. This layer may be e.g. a bismuth layer evaporated onto the base electrode, or a layer of selenide which is produced e.g. on -a nickel-plated iron base plate by depositing a slight lamount of selenium and heating it to temperatures of about 300 C.

The construction of rectier plates according -to the invention will now be brieliy explained with reference to the accompanying drawing wherein the figures show several embodiments of selenium layer arrangement.

In the most simple case, as is illustrated in Fig. 1, the rectier plate consists of a metallic base plate 1, ofa

selenium layer 2, which contains gallium and halogen, n

and of a metallic counter electrode 3. It is to be understood that the thicknesses of the layers, for reasons of clarity, are exaggerated and may not be taken as a scale for the true thickness ratio. The hatched layer indicates the gallium-containing selenium layer.

. According to Fig. 2, the selenium rectifier plate consists of the base plate or electrode 1, of the galliurnand halogen-containing selenium layer 2a, of the halogencontaining selenium layer 2b, and of the counter elec-` trode 3.

In the embodiment according to Fig. 3, th'e selenium layer consists of three partial layers, of which the layer 2a contains galliurn and halogen, and of which the layers 2b contain halogen only.

The embodiment yaccording to Fig. 4 resembles in principle the structure of the embodiment according to Fig. 3, with the exception that `an intermediate layer, e.g. of bismuth, is inserted between the base electrode 1V and the lowest selenium layer.

Finally, the rectiiier plate according to Fig. 5 consists of a metallic base electrode 1, eg. of iron, of an intermediate layer of metal e.g. of nickel 1b, `arnanged on said first layer, of a selenide layer 1c, e.g. of nickelselenide, of the halogen-containing selenium layer 2b, further of the halogenand gallium-containing selenium layer 2a, on which is arranged a halogen-containing selenium layer 2b. Between the counter electrode 3 and the uppermost selenium layer there is arranged an artiiicial barrier layer 4, e.g. of a suitable lacquer.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

11. A selenium rectier comprising a base electrode, a selenium layer including additives and a counter electrode, characterized in that the additives are halogen and gallium.

2. A selenium rectifier as claimed in claim l, characterized in that the concentration of gallium decreases from the side of the base electrode towards the side of the counter electrode.

3. A selenium rectifier as claimed in claim l, characterized in that said selenium layer comprises two portions and that only one portion contains gallium.

4. A selenium rectiier as claimed in claim 3, characterized in that a gallium-containing selenium layer is adjacent the base electrode.

5. A selenium rectifier as in claim 3, further characterized in that said one portion contains a maximum of l0 mg. of gallium per 100 g. of selenium.

6. A selenium rectiiier according to claim l, characterized in that said selenium layer contains up to approximately l5 mg. chlorine and up to approximately l0 mg. of gallium per v10() g. of selenium.

No references cited. 

1. A SELENIUM RECTIFIER COMPRISING A BASE ELECTRODE, A SELENIUM LAYER INCLUDING ADDITIVES AND A COUNTER ELECTRODE, CHARACTERIZED IN THAT THE ADDITIVES ARE HALOGEN AND GALLIUM. 